1. Field of the Invention
The invention relates to a system for automatically positioning the shape sensing roll of a metal strip rolling mill so as to maintain the proper wrap angle of the metal strip on the shape sensing roll. More specifically, the invention relates to such a system which includes a processor means for determining the appropriate wrap angle of the metal strip on the shape sensing roll, and hydraulic means for positioning the shape sensing roll, the hydraulic means being under the control of a servo means which receives actuating inputs from said processor means.
2. Description of Prior Art
In metal strip rolling mills, in order to determine whether the metal strip has the proper shape parameters such as gauge, level, bend, flatness, etc., the metal strip is led over a shape sensing roll where the parameters are measured, whereby to provide information for adjusting the mill for correction of the shape of the metal strip. The shape sensing roll typically comprises a plurality of side-by-side sensors as illustrated, for example, in U.S. Pat. No. 3,334,508, Martin, Aug. 8, 1967.
An important consideration in a system such as illustrated in the Martin patent is the wrap angle of the metal strip on the shape sensing roll. The wrap angle is defined as the angle subtended at the center of the shape sensing roll between the two points at which the metal strip is tangent to the shape sensing roll. If the wrap angle is too small, then the metal strip will not exert enough pressure on the shape sensing roll for the sensors to detect the pressure so that the shape sensing roll will not be able to perform its control function. If the wrap angle is too large, then the metal strip will exert enough pressure to do permanent damage to the sensors of the shape sensing rolls as the sensors are relatively fragile instruments.
As illustrated in U.S. Pat. No. 4,339,934, Mitchell, July 20, 1982, of which the present invention is an improvement, the wrap angle on the shape sensing roll 24 will change as a greater amount of strip is wrapped on the tension take-up reel 28. As can be seen, when there is only a small amount of metal strip coiled on the take-up reel, then the wrap angle on 24 is relatively large. However, as the amount of the coiled metal strip increases, the wrap angle decreases. Accordingly, it is possible to go from an appropriate size wrap angle to a wrap angle size which is too small.
One of the solutions of the prior art is to vertically position the shape sensing roll, relative to the position of the take-up reel, in a compromise manner, i.e., so that the range of wrap angles from start to finish is adequate, but only for a very small period of this time is the size of the wrap angle at its optimum. The positioning of the shape sensing roll is accomplished with a mechanism which includes side plates, with precisely located notches, on either side of the shape roll. The mechanism is rigidly fixed in position as it is necessary to ensure that the shape sensing roll remains horizontal at all times. If the shape sensing roll strays from the horizontal, then the measurements it records will not be accurate.
A problem with this approach is that it does represent a compromise solution instead of an optimum one. In addition, the vertical positions which the shape sensing roll can occupy are predetermined and cannot easily be altered. If the compromise lies somewhere between these discrete predetermined positions, then the compromise will not even be an optimum compromise.
A far better solution to the problem is the one illustrated in the Mitchell patent. Specifically, the Mitchell patent employs a hold-down roll 30 which is downstream of the shape sensing roll 24. As can be seen in the single drawing of the Mitchell patent, although the wrap angle on the hold-down roll will change as the coil of metal strip on the take-up reel increases, the wrap angle on the shape sensing roll will remain constant, this angle being fixed by the position of the hold-down roll 30 relative to the position of the shape sensing roll 24.
While the Mitchell solution does constitute an excellent response to the problem, there is one difficulty that the Mitchell solution does not overcome. Specifically, it is well known in the art that the appropriate wrap angle is a function of the gauge of the strip and the tension on the strip between the mill and the take-up reel. As these factors will vary from run to run, it is desirable to have a system whereby the wrap angle of the metal strip on the shape sensing roll can be varied. As it appears that the position of the hold-down roll in Mitchell is fixed in its operating condition, variation of the wrap angle would not be possible in the patented system.
In addition, the Mitchell solution requires the addition of a further roll, namely, the hold-down roll. As all rolls contacting the sheet have the ability to cause marks at one time or another, the addition of a further roll constitutes a disadvantage. Further, the additional roll will make system alignment more difficult.
In accordance with the present invention, the wrap angle will be made variable by providing means for continuously changing the vertical position of the shape sensing roll. The positioning means comprise hydraulic means, on either side of the shape sensing roll, under the control of MOOG servo position actuators which are accurate to within 0.005 in. That is, the height at either end of the shape sensing roll will be within 0.005 in. of the height of the other end, so that the roll remains substantially horizontal.
Means for altering the position of rolls in rolling mills are well known. The discrete position mechanical means as above described is one of these apparatus. A further apparatus is illustrated in U.S. Pat. No. 4,232,540, Cain et al, Nov. 11, 1980. The Cain et al patent teaches a hydraulic means 52, under the control of a servo valve 58, for altering the position of bending roll 16. However, the roll positioning means of Cain et al operate in an open loop system, and it does not operate on the shape sensing roll whose requirements are far different from the requirements of the bending roll.